The present invention relates generally to substrate processing chambers, and, in particular, to a gas inlet manifold or shower head for such chambers.
Glass substrates are being used for applications such as active matrix television and computer displays, among others. Each glass substrate can form multiple display monitors each of which contains more than a million thin film transistors.
The glass substrates can have dimensions, for example, of 550 mm by 650 mm. The trend, however, is toward even larger substrate sizes, such as 650 mm by 830 mm and larger, to allow more displays to be formed on the substrate or to allow larger displays to be produced. The larger sizes place even greater demands on the capabilities of the processing systems.
The processing of large glass substrates often involves the performance of multiple sequential steps, including, for example, the performance of chemical vapor deposition (CVD) processes, physical vapor deposition (PVD) processes, or etch processes. Systems for processing glass substrates can include one or more process chambers for performing those processes.
Plasma-enhanced chemical vapor deposition (PECVD) is another process widely used in the processing of glass substrates for depositing layers of electronic materials on the substrates. In a PECVD process, a substrate is placed in a vacuum deposition chamber equipped with a pair of parallel plate electrodes. The substrate generally is mounted on a susceptor which also serves as the lower electrode. A flow of a reactant gas is provided in the deposition chamber through a gas inlet manifold or shower head which also serves as the upper electrode. A radio frequency (RF) voltage is applied between the two electrodes which generates an RF power sufficient to cause a plasma to be formed in the reactant gas. The plasma causes the reactant gas to decompose and deposit a layer of the desired material on the surface of the substrate body. Additional layers of other electronic materials can be deposited on the first layer by flowing another reactant gas into the chamber. Each reactant gas is subjected to a plasma which results in the deposition of a layer of the desired material.
Though such systems are designed to deposit the material preferentially onto the surface of the substrate, some material is also deposited onto other interior surfaces within the chamber. After repeated use, the systems must be cleaned to remove the deposited layer of material that has built up in the chamber. To clean the chamber and the exposed components within the chamber, an in-situ dry cleaning process is sometimes used. According to one in-situ technique, precursor gases are supplied to the chamber. Then, by locally applying a glow discharge plasma to the precursor gases within the chamber, reactive species are generated. The reactive species clean the chamber surfaces by forming volatile compounds with the material deposited on those surfaces.
The foregoing in-situ cleaning technique has several disadvantages. First, it is inefficient to use a plasma within the chamber to generate the reactive species. Thus, it is necessary to use relatively high powers to achieve an acceptable cleaning rate. The high power levels, however, tend to produce damage to the hardware inside of the chamber thereby significantly shortening its useful life. Since the replacement of the damaged hardware can be quite costly, this can significantly increase the per substrate cost of a product that is processed using the deposition system. In the current, highly competitive semiconductor fabrication industry where costs per substrate are critical to the cost conscious purchasers, the increased operating costs resulting from periodically having to replace parts that are damaged during the cleaning process is very undesirable.
Another problem with the conventional in-situ dry cleaning processes is that the high power levels required to achieve acceptable cleaning rates also tend to generate residues or byproducts that can damage other system components, or which cannot be removed except by physically wiping off the internal surfaces of the chamber. As an example, in a deposition system in which the chamber or the process kit components (e.g. heater, shower head, clamping rings, etc.) are made of aluminum, a nitrogen fluoride (NF.sub.3) plasma is often used to clean the interior surfaces. During the cleaning process, a certain amount of aluminum fluoride (Al.sub.x F.sub.y) is formed. The amount that is formed is increased significantly by the ion bombardment that results from the high plasma energy levels. Thus, a considerable amount of Al.sub.x F.sub.y can be formed in the system and must be removed by physically wiping the surfaces.
A different technique for cleaning a process chamber is described in the previously mentioned U.S. patent application Ser. No. 08/707,491. The technique described in that application includes delivering a precursor gas into a remote chamber that is outside of the deposition chamber and activating the precursor gas in the remote chamber to form a reactive species. Activation of the precursor gas, which can include, for example, NF.sub.3, is performed by using a remote activation source. The reactive species flows from the remote chamber into the deposition chamber and is used to clean the inside of the deposition chamber. Using a remote plasma source can reduce or eliminate the damage that occurs during the cleaning process.
As already mentioned, the shower head in some of the foregoing systems is formed from aluminum. Conventionally, the surface of the aluminum shower head in in-situ chambers is anodized to maintain its reliability. For example, the shower head can be anodized by dipping it into sulfuric acid, thereby forming a layer of aluminum oxide (Al.sub.2 O.sub.3) over the surface of the shower head. One disadvantage of using an anodized aluminum shower head in a system having a remote plasma source is that the anodized aluminum appears to deactivate a significant amount of the fluorine radicals that form when the precursor gas NF.sub.3 is activated. The result is that the rate at which the chamber can be cleaned is reduced.